That's it. I think your issue must be something else. Make sure your
stop/start dovecot after each update or it will refuse to provide
access to mail.

Yep. I do that for every change to dovecot.conf.

BTW, I want to be able to use TLS and encrypted passwords. Thunderbird
complains about unencrypted passwords, but if I try to enable them, I
can't connect at all. There also seems to be an issue with creating
folders. So far, I have been able to create one, 1, count 'em one. No
sent or drafts folders either.